The inventive concepts described herein relate to a contactless thickness measuring apparatus and a thickness measuring method thereof.
A frequency (e.g., 0.1 to 10.0 THz) of a terahertz wave may correspond to a frequency domain of vibration and rotation among molecules of an organic/nonorganic material. In particular, the frequency may be associated with information of a living body material including moisture. In a terahertz spectroscopy, application to medical diagnosis, biotechnology material, etc. may be researched by using a characteristic not analyzed by another spectrum technique. In general, a terahertz wave may be generated using a pulse wave or a continuous wave.
A terahertz time-domain spectroscopy may use a pulse wave to analyze a material. Since signal amplitude and phase are simultaneously analyzed, it is possible to calculate a thickness or permittivity of a material. However, since a terahertz pulse-type spectrum system uses a high-priced femtosecond laser, its size may be large and high-priced. A terahertz frequency-domain spectroscopy developed to overcome the above-described drawback may use a terahertz continuous wave to analyze a material. Thus, in comparison with a pulse type spectroscopy, it is possible to implement a small-sized and low-priced system.
Since a terahertz continuous wave spectrum system generates and detects a terahertz wave using a beating light source of a laser having two different wavelengths, a terahertz wave generated may be decided by a beating frequency of the laser. A general terahertz continuous wave spectrum system may measure a thickness of a material in a homodyne manner by controlling a frequency of a terahertz continuous wave precisely. To achieve this, it is essential to perform precise control and measurement on a laser wavelength by which a terahertz continuous wave frequency is decided.